We recently encountered this problem in our San Francisco office, where a user reported that all the model elements have been deleted in a project. Do we need to restore the model from backup, rollback the worksets, contact Autodesk and report a bug...? First let's examine the scenario...
One team member had been working on the same model, but their immediate task was simply to perform some editing to annotation; therefore, they had closed all the User worksets. Remember, when you open a workset-enabled file, you can click the dropdown arrow next to the Open button to select the Specify option:
With the Specify setting, you can select all the User-Created worksets and set their Opened status to No (select them all in the list, then click Close).
This is good for performance, but obviously not good if you actually need to see some of the model components as you work!
Back to our story...this user synchronized with central and then another user began to perform some work. Now, this scenario should not affect anyone who is currently working in the same project model, but I presume it may be related to the script file our project teams use to automatically create new local copies. If user #1 had synchronized with all worksets closed, and then user #2 created a new local copy of the model and opened the model with the default workset option (Last Viewed), they might have all User-Created worksets turned off without the benefit of the Opening Worksets dialog box to indicate what is open or closed.
What's the moral of this story? We strongly recommend using the Specify option EVERY time you open a local copy of a project model. Remember you can also set the default action for opening when you first create a central file. Click on Options, and set the Open Workset Default to Specify as shown below. You can also check out one of our previous posts with other valuable tips on finding hidden elements.